Rocket motor assemblies generally include at least one containment vessel (e.g., housing) having at least one propellant structure (e.g., a solid propellant grain) therein, and at least one thrust nozzle operatively associated with the containment vessel. Multi-stage rocket motor assemblies may, for example, include an outer housing holding a plurality of stages each including a containment vessel holding a propellant structure therein, and a thrust nozzle operatively associated with the containment vessel. The outer housing may be separable such that when a propellant structure of a given stage has been consumed, that stage may be separated from the other stages to remove excess weight and, hence, increase the range and/or the speed of the multi-stage rocket motor assembly. An adjoining stage may then be fired immediately, or at a desired later time during the flight of the multi-stage rocket motor assembly.
Rocket motor assemblies can also include flexible bearing assemblies operatively associated with the thrust nozzles thereof. Each stage of a multi-stage rocket motor assembly may, for example, include a different flexible bearing assembly operatively associated with the thrust nozzle thereof. A flexible bearing assembly may include a lamination of alternating flexible seals and rigid shims that are stacked and bonded together. The lamination may be laterally flexible, that is, in directions parallel to the flexible seals, but unyielding in the directions perpendicular to the flexible seals. Lateral movement of the flexible bearing assembly (e.g., by way of at least one actuator) may be used to modify the orientation of the thrust nozzle operatively associated therewith, so as to control the direction of the rocket motor assembly during use and operation (e.g., flight) of the rocket motor assembly.
Unfortunately, the material compositions and properties of conventional flexible seals for flexible bearing assemblies can impose undesirable limitations on production efficiency, and on at least one of the capabilities, performance, durability, and reliability of the flexible bearing assemblies (and, hence, on rocket motor assemblies including the flexible bearing assemblies). For example, conventional flexible seals formed from natural rubber (NR) based formulations or polyisoprene (PI) rubber-based formulations may have significant production costs associated with the large number of ingredients beyond NR and PI (e.g., additives, such as fillers, antioxidants, tackifiers, processing aids, plasticizers, activations, curatives, etc.) typically required to achieve desirable properties, and can also have low strength, be prone to significant cavitation and loading damage, exhibit poor low temperature capabilities, and exhibit poor aging characteristics. As another example, conventional flexible seals formed from silicone rubber formulations including a single, preselected grade of silicone rubber can only be used for a very limited number of rocket motor assembly types due to the unsuitability of various material properties (e.g., Shore A hardness, shear modulus, etc.) provided by the selected grade of silicone rubber relative to the various needs (e.g., various loading needs, various torquing needs, etc.) of other, different rocket motor assemblies.
Accordingly, there is a continuing need for flexible structures (e.g., flexible seals) having material compositions and properties capable of meeting the needs of a wide variety of rocket motor assemblies, as well as for methods of forming such flexible structures. It would also be desirable to have new assemblies (e.g., flexible assemblies, moveable thrust nozzle assemblies, rocket motor assemblies, etc.) including such flexible structures.